[PATCH 1/1] i2c: at91: constify at91_twi_pdata

[PATCH 1/1] i2c: at91: constify at91_twi_pdata

[Michał Mirosław]

Signed-off-by: Michał Mirosław <mirq-linux@rere.qmqm.pl>
---
 drivers/i2c/busses/i2c-at91-core.c   | 24 ++++++++++++------------
 drivers/i2c/busses/i2c-at91-master.c |  4 ++--
 drivers/i2c/busses/i2c-at91.h        |  2 +-
 3 files changed, 15 insertions(+), 15 deletions(-)

diff --git a/drivers/i2c/busses/i2c-at91-core.c b/drivers/i2c/busses/i2c-at91-core.c
index 05ad3bc3578a..4d484e231371 100644
--- a/drivers/i2c/busses/i2c-at91-core.c
+++ b/drivers/i2c/busses/i2c-at91-core.c
@@ -62,28 +62,28 @@ void at91_init_twi_bus(struct at91_twi_dev *dev)
 		at91_init_twi_bus_master(dev);
 }
 
-static struct at91_twi_pdata at91rm9200_config = {
+static const struct at91_twi_pdata at91rm9200_config = {
 	.clk_max_div = 5,
 	.clk_offset = 3,
 	.has_unre_flag = true,
 };
 
-static struct at91_twi_pdata at91sam9261_config = {
+static const struct at91_twi_pdata at91sam9261_config = {
 	.clk_max_div = 5,
 	.clk_offset = 4,
 };
 
-static struct at91_twi_pdata at91sam9260_config = {
+static const struct at91_twi_pdata at91sam9260_config = {
 	.clk_max_div = 7,
 	.clk_offset = 4,
 };
 
-static struct at91_twi_pdata at91sam9g20_config = {
+static const struct at91_twi_pdata at91sam9g20_config = {
 	.clk_max_div = 7,
 	.clk_offset = 4,
 };
 
-static struct at91_twi_pdata at91sam9g10_config = {
+static const struct at91_twi_pdata at91sam9g10_config = {
 	.clk_max_div = 7,
 	.clk_offset = 4,
 };
@@ -110,19 +110,19 @@ static const struct platform_device_id at91_twi_devtypes[] = {
 };
 
 #if defined(CONFIG_OF)
-static struct at91_twi_pdata at91sam9x5_config = {
+static const struct at91_twi_pdata at91sam9x5_config = {
 	.clk_max_div = 7,
 	.clk_offset = 4,
 };
 
-static struct at91_twi_pdata sama5d4_config = {
+static const struct at91_twi_pdata sama5d4_config = {
 	.clk_max_div = 7,
 	.clk_offset = 4,
 	.has_hold_field = true,
 	.has_dig_filtr = true,
 };
 
-static struct at91_twi_pdata sama5d2_config = {
+static const struct at91_twi_pdata sama5d2_config = {
 	.clk_max_div = 7,
 	.clk_offset = 3,
 	.has_unre_flag = true,
@@ -134,7 +134,7 @@ static struct at91_twi_pdata sama5d2_config = {
 	.has_clear_cmd = false,	/* due to errata, CLEAR cmd is not working */
 };
 
-static struct at91_twi_pdata sam9x60_config = {
+static const struct at91_twi_pdata sam9x60_config = {
 	.clk_max_div = 7,
 	.clk_offset = 3,
 	.has_unre_flag = true,
@@ -181,7 +181,7 @@ static const struct of_device_id atmel_twi_dt_ids[] = {
 MODULE_DEVICE_TABLE(of, atmel_twi_dt_ids);
 #endif
 
-static struct at91_twi_pdata *at91_twi_get_driver_data(
+static const struct at91_twi_pdata *at91_twi_get_driver_data(
 					struct platform_device *pdev)
 {
 	if (pdev->dev.of_node) {
@@ -189,9 +189,9 @@ static struct at91_twi_pdata *at91_twi_get_driver_data(
 		match = of_match_node(atmel_twi_dt_ids, pdev->dev.of_node);
 		if (!match)
 			return NULL;
-		return (struct at91_twi_pdata *)match->data;
+		return match->data;
 	}
-	return (struct at91_twi_pdata *) platform_get_device_id(pdev)->driver_data;
+	return (const void *) platform_get_device_id(pdev)->driver_data;
 }
 
 static int at91_twi_probe(struct platform_device *pdev)
diff --git a/drivers/i2c/busses/i2c-at91-master.c b/drivers/i2c/busses/i2c-at91-master.c
index c0c35785a0dc..0434aabb66fe 100644
--- a/drivers/i2c/busses/i2c-at91-master.c
+++ b/drivers/i2c/busses/i2c-at91-master.c
@@ -32,7 +32,7 @@
 
 void at91_init_twi_bus_master(struct at91_twi_dev *dev)
 {
-	struct at91_twi_pdata *pdata = dev->pdata;
+	const struct at91_twi_pdata *pdata = dev->pdata;
 	u32 filtr = 0;
 
 	/* FIFO should be enabled immediately after the software reset */
@@ -67,7 +67,7 @@ void at91_init_twi_bus_master(struct at91_twi_dev *dev)
 static void at91_calc_twi_clock(struct at91_twi_dev *dev)
 {
 	int ckdiv, cdiv, div, hold = 0, filter_width = 0;
-	struct at91_twi_pdata *pdata = dev->pdata;
+	const struct at91_twi_pdata *pdata = dev->pdata;
 	int offset = pdata->clk_offset;
 	int max_ckdiv = pdata->clk_max_div;
 	struct i2c_timings timings, *t = &timings;
diff --git a/drivers/i2c/busses/i2c-at91.h b/drivers/i2c/busses/i2c-at91.h
index 942e9c3973bb..f0c80b89e502 100644
--- a/drivers/i2c/busses/i2c-at91.h
+++ b/drivers/i2c/busses/i2c-at91.h
@@ -147,7 +147,7 @@ struct at91_twi_dev {
 	unsigned transfer_status;
 	struct i2c_adapter adapter;
 	unsigned twi_cwgr_reg;
-	struct at91_twi_pdata *pdata;
+	const struct at91_twi_pdata *pdata;
 	bool use_dma;
 	bool use_alt_cmd;
 	bool recv_len_abort;
-- 
2.39.2

Re: [PATCH 1/1] i2c: at91: constify at91_twi_pdata

[Andi Shyti]

Hi Michal,

[...]

> -static struct at91_twi_pdata *at91_twi_get_driver_data(
> +static const struct at91_twi_pdata *at91_twi_get_driver_data(
>  					struct platform_device *pdev)
>  {
>  	if (pdev->dev.of_node) {
> @@ -189,9 +189,9 @@ static struct at91_twi_pdata *at91_twi_get_driver_data(
>  		match = of_match_node(atmel_twi_dt_ids, pdev->dev.of_node);
>  		if (!match)
>  			return NULL;
> -		return (struct at91_twi_pdata *)match->data;
> +		return match->data;
>  	}
> -	return (struct at91_twi_pdata *) platform_get_device_id(pdev)->driver_data;
> +	return (const void *) platform_get_device_id(pdev)->driver_data;

the const's always confuse me... do you get an error here? Is
this cast really needed?

Andi

Re: [PATCH 1/1] i2c: at91: constify at91_twi_pdata

[Michał Mirosław]

On Fri, Jun 30, 2023 at 12:38:25AM +0200, Andi Shyti wrote:
> Hi Michal,
> 
> [...]
> 
> > -static struct at91_twi_pdata *at91_twi_get_driver_data(
> > +static const struct at91_twi_pdata *at91_twi_get_driver_data(
> >  					struct platform_device *pdev)
> >  {
> >  	if (pdev->dev.of_node) {
> > @@ -189,9 +189,9 @@ static struct at91_twi_pdata *at91_twi_get_driver_data(
> >  		match = of_match_node(atmel_twi_dt_ids, pdev->dev.of_node);
> >  		if (!match)
> >  			return NULL;
> > -		return (struct at91_twi_pdata *)match->data;
> > +		return match->data;
> >  	}
> > -	return (struct at91_twi_pdata *) platform_get_device_id(pdev)->driver_data;
> > +	return (const void *) platform_get_device_id(pdev)->driver_data;
> 
> the const's always confuse me... do you get an error here? Is
> this cast really needed?

platform_device_id.driver_data is an ulong, not a void pointer. So, the
cast is needed. It could be just (void *), but I think it's better to
document the constness in the code.

-- 
Michał Mirosław

Re: [PATCH 1/1] i2c: at91: constify at91_twi_pdata

[Krzysztof Kozlowski]

On 30/06/2023 00:38, Andi Shyti wrote:
> Hi Michal,
> 
> [...]
> 
>> -static struct at91_twi_pdata *at91_twi_get_driver_data(
>> +static const struct at91_twi_pdata *at91_twi_get_driver_data(
>>  					struct platform_device *pdev)
>>  {
>>  	if (pdev->dev.of_node) {
>> @@ -189,9 +189,9 @@ static struct at91_twi_pdata *at91_twi_get_driver_data(
>>  		match = of_match_node(atmel_twi_dt_ids, pdev->dev.of_node);
>>  		if (!match)
>>  			return NULL;
>> -		return (struct at91_twi_pdata *)match->data;
>> +		return match->data;
>>  	}
>> -	return (struct at91_twi_pdata *) platform_get_device_id(pdev)->driver_data;
>> +	return (const void *) platform_get_device_id(pdev)->driver_data;
> 
> the const's always confuse me... do you get an error here? Is
> this cast really needed?

I think this change is not necessary and actually should not matter. See
for example drivers/tty/serial/samsung_tty.c after my refactorings in
commit 3aec40096550 ("tty: serial: samsung: reduce number of casts").

Best regards,
Krzysztof

Re: [PATCH 1/1] i2c: at91: constify at91_twi_pdata

[Michał Mirosław]

On Mon, Jul 03, 2023 at 08:23:30PM +0200, Krzysztof Kozlowski wrote:
> On 30/06/2023 00:38, Andi Shyti wrote:
> > Hi Michal,
> >> -static struct at91_twi_pdata *at91_twi_get_driver_data(
> >> +static const struct at91_twi_pdata *at91_twi_get_driver_data(
> >>  					struct platform_device *pdev)
> >>  {
> >>  	if (pdev->dev.of_node) {
> >> @@ -189,9 +189,9 @@ static struct at91_twi_pdata *at91_twi_get_driver_data(
> >>  		match = of_match_node(atmel_twi_dt_ids, pdev->dev.of_node);
> >>  		if (!match)
> >>  			return NULL;
> >> -		return (struct at91_twi_pdata *)match->data;
> >> +		return match->data;
> >>  	}
> >> -	return (struct at91_twi_pdata *) platform_get_device_id(pdev)->driver_data;
> >> +	return (const void *) platform_get_device_id(pdev)->driver_data;
> > 
> > the const's always confuse me... do you get an error here? Is
> > this cast really needed?
> 
> I think this change is not necessary and actually should not matter. See
> for example drivers/tty/serial/samsung_tty.c after my refactorings in
> commit 3aec40096550 ("tty: serial: samsung: reduce number of casts").

I added this two fragments to avoid having suggesting that the pdata might
not be in a read-only segment.  For the compiler it doesn't matter -- the
pointer is cast to const on return.

Best Regards
Michał Mirosław